1. Field of the Invention
The present invention relates to an ink jet printhead which is used as an printing portion of a printer, facsimile machine, plotter or the like.
2. Description of the Prior Art
An ink jet printhead of the above-described type is disclosed in Japanese Patent Application Laid-open No. 5-254140 (particularly, FIG. 3 thereof) for example. For the convenience of description, the ink jet printhead disclosed in this document is illustrated in FIGS. 15 and 16 of the accompanying drawings.
As shown in FIG. 15, the prior art ink jet printhead has a rectangular head body 1e formed with ink inlet ports 8e at predetermined peripheral positions 19a-19d of the head body (four corners of the head body 1 in FIG. 15). These ink inlet ports 8e are connected to four common ink passages 50e, and these common ink passages 50e are connected to a plurality of individual ink passages 51e provided in radial arrangement. Further, the head body 1e has a front surface formed with a plurality of discharge ports 55e communicating with the corresponding discharge ports 55e.
The four ink inlet ports 8e are independent of each other. Therefore, if inks of different colors including yellow, magenta (red), cyan (blue) and black are supplied through the ink inlet ports 8e, it is possible to perform desired color printing.
As shown in FIG. 16 for example, the head body 1e comprises a passage forming panel 10e made of glass, and a vibration plate 11e laminated on the passage forming panel. The passage forming panel 10e has one surface formed with grooved ink passages 5e which includes the above-mentioned individual ink passages 51e and common ink passages 50e. Further, the vibration plate 11e has a rear surface provided with piezoelectric elements 13 by intervention of a conductor layer 12 which is made of ITO film (tin oxide film containing a small amount of additives or indium oxide film containing tin oxide) for example. When the vibration plate 11e is flexibly deformed in the direction of arrow N2 by application of a voltage to each of the piezoelectric elements 13, the volume of the corresponding ink passage 5e instantaneously decreases to discharge the inside ink of the ink passage 5e through the corresponding nozzle port 55e as an ink droplet.
With the prior art ink jet printhead, each of the grooved ink passages 5e is extended to an outer edge 19a (or 19b-19d) of the head body 1e to form an ink inlet port 8e. Therefore, the ink passage 5e tends to be long, consequently leading an increase of resistance against ink flow.
On the other hand, if air (foams) gets in the ink inside the ink passages 5e, it is necessary to connect e.g. a suction device to the nozzle ports 55e for discharging out the foams together with the ink inside the ink passages 5e. However, in the prior art ink jet printhead, since the ink passages 5e are long, the wasted amount of ink discharged with the foams becomes large. Further, as the ink passages 5e become longer, the operation of discharging the inside foams gets more difficult.
Moreover, ink need be supplied from around the head body 1e for introducing the ink into the ink inlet ports 8e which are open radially of the head body 1e, as indicated by arrows N in FIG. 15. Thus, the structure for connecting the ink passages 5e of the head body 1e to the surrounding ink supply paths becomes complicated, and difficulty arises in sealing. As a result, the resistance to ink flow may vary greatly from one passage to another (which causes uneven discharge of ink droplets), and ink leakage is likely to occur. Further, there is also the problem of a manufacturing cost increase.